Apparatus for electrically measuring thicknesses



u 6, 1950 2 G. cor Em. 2,510,822

' APPARATUS FOR ELECTRICALLY MEASURING THICKNESSES Filed Feb. 5, 1945 Z g B Y A Z 0 2 A E L |||T lllllllllll IIIIIFIIIIII! ///////////l I W VII/l/l/ll/AIM Invewlord, Georges (721cc? 21ml Jean Monti Patented June 6,

APPARATUS FOR ELECTRICALLY MEASURING THICKNESSES Georges Jacot and Jean Monti, Geneva,

witzerland AppllcatiiiiliFebr-uary 5, 1946, Serial No. 645,589

The object of the present invention is an apparatus for measuring thicknesses with great accuracy.

The accompanying drawing shows diagrammatically and by way of examples, two forms of this apparatus in Figure l and in Figure 2 respectively.

In the drawing, A is the rod of a comparator F reading to one hundredth of a millimetre, mechanically operated in a well known way.

E represents a standard thickness block resting on a support M. The rod A is fixed to the plate C of a linear variation electric measuring condenser, which is capable of being raised or lowered in relation to the other plate B of this condenser; the two plates are tubular. At D is an insulating layer.

The raising or lowering of the plate C efiects a variation of the capacity which can be measured with a very great degree of accuracy in making use of an oscillating circuit such as the one.indicated on the drawing, which includes a thermionic tube R of the pentode type having a cathode I, a control grid 2, a screen grid 3, a protection grid 4, which is joined interiorly to the cathode I, and an anode 5. The quartz crystal Q is connected between the cathode I and the grid 2 of the tube R. As shown, the tunable oscillating anodecircuit of tube R includes the inductance coil L, a compensating'linear variable condenser C1 having tubularplates and provided with means (Fig. 2) operable with the movable element thereof for indicating variations thereof, and the variable measuring condenser B, C connected across the cathode l and the anode 5.

The quartz crystal connected acrossthe cathode I and the grid 2 generates oscillations which set up in the anode circuit a high frequency oscillating current depending upon the characteristics of the crystal. It will be noted that grid 3 is connected to a source of positive potential for applying such potential to said grid.

Each variation of capacity of the condenser B, C disturbs the tuning of the oscillating circuit and, in order to restore the electrical balance, the capacity of C1 must be varied, so as to compensate the variation of B, C. Each difference of thickness of E produces a linear variation of the capacity of B, C. The out of tuning is indicated by a milli-ammeter I.

B, C and C1 being absolutely linear, one can gauge C1 directly in fractions of one thousandth of a millimetre, as indicated in Fig. 2.

a condenser C11 is provided in a circuit across witzerland May 15, 1945 1 Claim. (Cl. 117-351) 2 4 the anode 5 and the grid 2 and serves only to neutralize the internal capacity of the tube R in order to obtain a better resonance curve and thus effect the regulation with a smaller variation of the condenser C1 and consequently with greater precision. It is necessary to adjust the condenser C11 only once and then no further adjustment is necessary.

The oscillator thus constituted is placed in a container within which the temperature remains constant.

The comparator F makes it possible to compare the standard block E with the part which is to be measured, by adjusting the engagement depth between themselves of the plates C, B.

Figure 2 embodies a device permitting the direct reading, arranged in such a way that the compensating condenser C1 include a mobile part,

'the displacements of which are automatically millimetre is automatically indicated by the meter 0 through a set of gears acting simultaneously on the said meter and on the mobile,

part of C1.

In order to avoid mistakes due to the personal factor, an electric brake operated by the apparatus itself by means of the electric circuit shown on the diagram, instantaneously stops the mechanism at the moment of going out of tune.

This electric circuit is placed between the ground and the positive high voltage pole of the oscillating circuit. The diiference of voltage brought about by the going outof tune of the oscillating circuit controls a tube P which operates on an electro-magnet S acting on a blocking device, as shown on the drawing, in order to cause the stopping of the reading device. 0n the drawing, the electro-magnet S attracts a flexible disc T which is fixed to the operating shaf What we claim as our invention and desire to I secure by Letters Patent of the United States is:

3 v thecathodeandoneoisaidlridaathirdvariable condenser connected between the anode and the zrid which is connected by the crystal to the cathode, means for applying a positive potential to another 01' said grids spaced from the grids connected by the crystal and third condenser to the cathode and anode, means responsive to the variations in thicknesses to be measured for varying the first condenser, and means operable with the second condenser for indicatin: the variation thereoi'.

GEORGES JACOT. JEAN MON'I'I.

REFERENCES CITED The following references are of record in the tile of this patent: V

4 UNITED STATES PATENTS Green Feb. 19, 1985 Arms et ai. June 11. 1935 Leonard July 28. 1935 Conover May 25. 193'! Temple June 15, 193'! Bight Apr. 5, 1988 Price Feb. I, 1939 Sivertsen Nov. 14. 1939 Woliskill Apr. 29. 1941 Shepard Apr. 21,1942

Pike et 91. Jill! '1. 1m 

